The invention relates to image forming systems, and more particularly relates to image forming systems that print objects in multiple swaths.
There are a number of different image forming systems in use today for generating images on a print medium. For example, one of those systems employs focused acoustic energy to eject droplets of marking material, such as ink, from a printhead onto a recording medium. This type of system utilizes printing technology known as acoustic ink printing, (AIP) systems.
Printheads utilized in AIP systems most often include a plurality of droplet ejectors, each of which emits a converging acoustic beam into a pool of fluid (e.g., ink). The angular convergence of this beam is selected such that the beam focuses at or near the free surface of the ink, in other words at the border between the ink and air. Printing is executed by modulating the radiation pressure that the beam of each ejector exerts against the free surface of ink to selectively eject droplets of ink from the free surface.
In the instance where color printing is desired, typically droplets of various different colored inks are ejected from one or more printheads. To achieve the wide variety of colors demanded for documents, differing numbers of droplets of each of the various color inks are positioned together to produce such colors. The most commonly occurring individual colors utilized for the different inks are cyan, magenta, yellow, and black. The colors that may result from differing combinations of the four colors are often identified as the CMYK gamut.
One consistent demand of conventional image forming systems is for image forming devices and systems that operate at greater and greater speeds. The speed at which printed output is produced is primarily a function of the number of passes the printhead is required to make over a particular printing medium. For a printer, the majority of colors can often be printed in a number of passes smaller than the maximum. However, more passes are necessary when any one of the printhead ejectors does not deliver the required ink to a requisite location prior to the printhead moving to a different location on the printing medium.
In many direct marking systems objects such as black text can be printed in a single pass. However, if there is a graphic object or colored text, for example, the printer defaults to multiple pass printing. This can have a significant impact on the visual quality of the black text. Given adequate directionality and ink which does not mottle at volume, that can allow objects other than black text to be printed in a single pass while still maintaining excellent image quality. A significant consideration as to whether to print in a single pass verses a multiple pass is the amount of ink required. While maximum color density is achieved with a full number of ejector droplets (for example, 10 droplets), a solid of 80% of the color reflectance can be printed with only five ejector ink droplets. In other words, a reasonably saturated color with excellent image quality can be achieved in only a single pass. Consequently, there is no need to checkerboard print objects that are within this limited gamut, except for maintaining consistency within the page or from page to page. This is not limited to one and two pass printing. For example, adequate inking and quality for some object might be achieved with two passes, while other objects require more than two passes. An issue arises when trying to exploit this situation. A single object to be printed, which requires only a single pass, may cross the border between two or more swaths. The object in one of the swaths may required only a single pass, and the remainder of the object in the other swath may require more than one pass, i.e., multiple passes. If a portion of the object is printed with a single pass and another portion of the object is printed with multiple passes, there exists the possibility of visual differences at the object boundary. Such visual differences include slight differences in color or texture. The rate at which ink droplets are fired from the printhead and/or the rate at which ink lands on the printing medium may generate these visual differences.
For the foregoing reasons, there exists in the art a need for an image forming system that takes advantage of possible print modes and preserves the integrity of objects that do not require the maximum number of passes. In general, the present invention provides for a method for printing a plurality of objects in an image with a printhead in an image forming system.
The method begins with the identification, by a computing apparatus or processor, of the objects in the image. The computing apparatus determines the minimum number of passes of the printhead required to print each object in the image. Then, the printhead prints each object in only the minimum number of passes determined to be required to properly print that object. If other objects in the same swath require a different minimum number of passes to be properly printed, they are printed in those minimum number of passes, regardless of the number of passes utilized to print the first object in the swath.
A more economical implementation does not require the identification of objects across swaths. Rather than splitting ink drops equally between passes, the maximum number of drops on one pass and the remainder (if more than the maximum) would be printed on other passes. Thus objects that require fewer drops are printed on a single pass, even if a swath requires multiple passes. If a pass requires no drops of ink, it can be skipped.
As a result, a method of gamut skipping proposes printing some swaths in a single pass and other swaths in multiple passes, the number of passes required per entire swath depends on the number of ink droplets required at each pixel within the swath. A method including these features is disclosed in U.S. application Ser. No. 09/440,424, entitled Choosing Print Passes and Speed Based on Required Number of Drops for Each Swath, filed Nov. 15, 1999, and incorporated herein by reference.
Another way to take advantage of objects that require fewer passes is to print such objects unidirectionally. For example, the object can be printed in one pass within a two pass document. The one pass can always be chosen to be the pass in either the left-to-right or the right-to-left direction.
The term xe2x80x9cgamut skippingxe2x80x9d as used herein, is intended to include any technique for skipping portions of the substrate or medium or reducing the time to print an image on the substrate. For example, the system can determine the fewest number of passes that are required to produce a desired output for each of the pixels in a particular swath. The term xe2x80x9cgamutxe2x80x9d as used herein is intended to describe all colors that are achievable by a printing device used in the image forming system. Similar to white-space skipping, another form of printing known to one of ordinary skill in the art, gamut skipping causes the printing device printhead to completely skip any passes that do not require ink to be laid on the printing medium. Gamut skipping is utilized when all pixel colors in the particular swath are within the gamut of earlier passes, and hence have already been achieved by earlier passes. Further, gamut skipping seeks to minimize the number of passes a device printhead makes over each swath.
In accordance with one example embodiment of the present invention, an ink printing system is provided. Such a system includes at least one printhead. In addition, there is a processor in electronic communication with the printhead. The processor receives information regarding a collection of objects to be printed and processes the information to direct a printing pattern such that objects printable in their entirety in a first number of passes are printed in the first number of passes. A remaining portion of the collection of objects is printed in a second, third, or fourth number of passes as required. Hence, the object within the image, rather than the entire image, determines the number of passes required to print the object within each swath.
According to another aspect of the present invention, if a particular object spans between multiple swaths, the number of passes utilized to print the object in the first swath is maintained throughout the printing of the object in the remaining swaths. This consistency is maintained regardless of another object existing in the remaining swaths that is printed in a different number of passes. Such other object is printed in the different number of passes.